The present invention relates to internal combustion engines and particularly to the treatment of blow-by gases in such engines.
Blow-by in internal combustion engines is the unwanted leakage of gas under pressure such as is known to occur past a piston and/or its sealing rings into the crankcase of the engine. The phenomenon generally results from the production of very high pressure conditions within the combustion chamber of the engine just after ignition which may cause typically small quantities of gas to leak through areas where an imperfect fluid seal may exist. Accordingly, as well as leakage into the crankcase of an engine, blow-by may also occur past intake or exhaust valves and injection elements located in the engine cylinder head or upper sections of the cylinder wall and into the volume beneath a cam or rocker cover of the engine.
Different emission control systems for dealing with such blow-by gases in order that they are prevented from entering the atmosphere are well known. The most common typically include a positive crankcase ventilation or PCV valve which enables blow-by gases in the crankcase to be drawn therefrom. Typically, such blow-by gases are fed to an appropriate location within the engine""s induction system, such as for example, a point upstream of the individual runners or air tracts which duct air to each cylinder. Such systems rely on the vacuum present in the induction system upstream of the engine cylinders to draw the blow-by gases from the crankcase and into the induction system. The blow-by gases are subsequently delivered by the induction system back into the combustion chambers of the engine for burning, together with the fresh air charge required for subsequent combustion events.
Further, in respect of the blow-by gases which may be present in the volume beneath any cam and/or rocker cover of the engine, it is know to provide a simple conduit communicating the volume beneath the cam or rocker cover with the engine induction system. In a similar manner, the vacuum generated in the induction system is used to draw any blow-by gases present in such volumes through the conduit and into the induction system such that they can be delivered to the engine combustion chambers.
In U.S. Pat. No. 5,669,366 (Beach et al), there is described a closed crankcase ventilation system for recycling blow-by gas that has accumulated within the engine crankcase. The engine includes a turbocharger, and the system relies on suction generated from a vacuum assist from the turbocharger inlet to draw blow-by gases from the crankcase. The blow-by gases are then delivered to the engine induction system for subsequent combustion within the engine combustion chambers.
Whilst the above mentioned prior art systems provide a simple way for treating any blow-by gases that may exist within certain parts of the engine, it has been found that under some circumstances, and in particular relation to certain engine applications, that they may not always satisfactorily deal with such blow-by gases. In particular, in certain engine applications, the level of vacuum which is present in the induction system under idle and low load conditions may not be enough to effectively draw any blow-by gases from their location within the engine into the induction system for subsequent delivery into the engine combustion chambers for burning. This is particularly so in regard to stratified charge engines which generally operate with a significantly lower level of vacuum in the induction system. In such engines, noticeable difficulty may be experienced in regard to the treatment of blow-by gases by way of such prior art systems. Similar problems may exist in regard to conventional four-stroke manifold injection engines except that the unsatisfactory levels of vacuum in the induction system may exist at medium to high engine operating loads.
Further there is a possibility in all of the abovedescribed arrangements that not all of the blow-by gases delivered by the engine induction system are unsatisfactorily burnt. This is because as the blow-by gases are mixed and thereby diluted in the bulk air delivered by the induction system to the engine, at least some of the hydrocarbons present in the blow-by gases may be delivered away from the main ignition area within the combustion chambers. These hydrocarbons may then not be satisfactorily burnt prior to being exhausted from the engine leading to unwanted hydrocarbon exhaust emissions.
It is therefore an object of the present invention to provide a method for the treatment of engine blow-by gases and an apparatus therefor which ameliorates at least some of the problems or short-comings of the prior art.
With this in mind, the present invention provides in one aspect a method of treating blow-by gases within an internal combustion engine, the engine including at least one combustion chamber, a dual fluid injection system for delivering a metered quantity of fuel entrained in compressed gas to the at least one combustion chamber, and a compressor for supplying the compressed gas, the method including using the intake vacuum of the compressor to draw the blow-by gases from within the engine for subsequent delivery by the injection system to the at least one combustion chamber.
Preferably, the compressor supplies pressurised gas, typically air, to entrain a metered quantity of fuel for delivery directly into the at least one combustion chamber. In this way, blow-by gases drawn from the engine by the compressor may be delivered directly into the combustion chamber by way of the dual fluid fuel injection system.
Because the blow-by gases are delivered from the compressor directly into the at least one combustion chamber of the engine by the fuel injection system, such blow-by gases may be satisfactorily burnt within the combustion chamber and/or suitably treated by an exhaust system of the engine. That is, this leads to more effective combustion of the blow-by gases because the hydrocarbons are delivered in a controlled manner into the combustion chamber as part of a fuel rich fuel spray.
Conveniently, the engine includes at least one cylinder supporting a piston therein, a cylinder head and a crankcase, the cylinder and the piston together with the cylinder head defining the combustion chamber. Conveniently, a rocker or cam cover may be associated with the cylinder head in the usual manner such that the rocker or cam cover and the cylinder head together define a volume beneath the rocker or cam cover.
Preferably, the blow-by gases are drawn by the compressor from the engine crankcase. Preferably, the blow-by gases are drawn by the compressor from the volume beneath the rocker or cam cover. Conveniently, the intake vacuum of the compressor may be used to draw blow-by gases simultaneously from both the engine crankcase and the rocker or cam cover volume.
The method may be implemented as the sole method for treating blow-by gases within the engine or may alternatively be used in conjunction with other known prior art systems or methods for treating blow-by gases such as those mentioned hereinbefore. Conveniently, the method is implemented when the engine is operating at idle and/or low loads.
Preferably, the method is implemented in a stratified charge engine. Such engines typically operate with a low level of vacuum in the induction system.
According to another aspect of the present invention, there is provided a system for treating blow-by gases within an internal combustion engine, the engine including at least one combustion chamber, a dual fluid injection system for delivering a metered quantity of fuel entrained in compressed gas to the at least one combustion chamber, a compressor for supplying the compressed gas, and means connecting an intake of the compressor with a part of the engine where blow-by gases may be present such that the intake vacuum of the compressor can draw the blow-by gases from within the engine for subsequent delivery by the injection system to the at least one combustion chamber.
Preferably, the compressor supplies pressurised gas, typically air, to entrain a metered quantity of fuel for delivery directly into the at least one combustion chamber.
Conveniently, the engine includes at least one cylinder supporting a piston therein, a cylinder head and a crankcase, the cylinder and the piston together with the cylinder head defining the combustion chamber. Conveniently, a rocker or cam cover may be associated with the cylinder head in the usual manner such that the rocker or cam cover and the cylinder head together define a volume beneath the rocker or cam cover.
Preferably, the part of the engine from which the blow-by gases are drawn is an engine crankcase. Preferably, the part of the engine from which the blow-by gases are drawn is the volume beneath the rocker or cam cover.